Injection of wax into rubber moulds

The advent of vacuum wax injection systems has, in recent years, largely superceded oldfashioned pressure injectors with their attendant problems of air inclusions, incomplete filling and difficulties in reproducing thin sections.

The latest units available are extremely reliable and accurate.

Pressure is supplied by an air com pressor and a small vacuum puml evacuates the mould, the vacuuminj time being controlled by a secon timer (fig. 16).

This, together with the injection period, is controlled electronically by a compact circuit board which also regulates wax chamber and nozzle temperatures.

The rubber mould is offered to the injector nozzle. The mould is then evacuated for one or more seconds and then the wax immediately injected. It is obvious that, under these conditions, the production of perfect waxes is automatic and high production rates of quality wax patems are achievable.

Air inclusions in the centre of wax patterns are generally of no importance but, near the surface, can burst under vacuum and appear as surface

defects in the finished castings, usually during surface treatment (fig. 18). These defects are frequently wrongly identified as porosity,

This is an additional advantage, as these vents frequently produce "finning" on the waxes which have to be removed prior to investing.

The vacuum injection process may be farther enhanced by the addition of an automatic clamping and feeding system, which clamps the mould, offers it to the nozzle during the vacuum/injection cycle and then re ts when injection is completed, final y unclamping after solidification fig. 19).